Tubing



July l0, 1945. R, H. HoBRocK TUBING Filed May- 2 1941 that nickel andcoppervery readily alloy vthe freezing point of Patented July 10, 1945 iTUBING Raymond H. Hobrock, Grosse Pointe, Mich., as-

signor to Bundy Tubing` Company, Detroit,

Mich., a corporation of Michigan Application May 2, 1941, Serial No.391,595 4 Claims. v(Cl. 13S-47) This invention relates to tubing, and ithas to do particularly with tubing having corrosion resistingproperties, tubing capable of being subjected to severe cold workingoperations, and to the method of making the tubing.

The principal object of the invention is to provide a tube and method ofmaking the tube, wherein the tube is fashioned from strip stock, some orall of which is a copper-nickel alloy, and wherein juxta-positionedparts of the stock, such as parts in a seam or seams or plies, areunited by the use of copper or a cuprous metal, which is rendered moltenin the process. It is appreciated by those skilled in the metal art witheach other, and this fact presents a difcult problem where it is desiredto seal or bond together, by the use of copper, two bodies of metal ortwo portions of a body of metal, at least one of which comprises anickel-copper alloy.

In accordance with the invention the amount of copper employed isrelatively small as compared with the amount of metal in thecoppernickel strip. If the metals are heated in a furnace where, forexample, even a minute or two is required to raise the metals to coppermelting temperature, the copper is completely absorbed by the nickelwith the result that there is no sealing or joining of thejuxta-positioned parts. This may occur by a diffusion of the metals inthek solid state without the copper having become molten, or it mayoccur with the copper in a melted state. The situation is va dynamicone, in that once the copper is rendered molten a rapid alloying of thecopper and nickel takes glace, resulting in an ever-increasing meltingpoint and requiring an increase in temperature to maintain the moltenstate. Yet the temperature must not exceed the `melting point of thecopper-nickel strip stock. .If the temperature is not increased afterthe copper becomes molten, the absorption of the nickel by the copperresults in the formation of a nickel-copper" alloy which freezes as itsmelting point reaches or exceeds the temperature, and this prevents theproper owing or migration of the copper into the seam or between plies,and' the failure to unite the juxta-positioned metal bodies or portions.

Accordingly, the invention contemplates and provides a method whereinthe rate of increase in the temperature, in the range above the meltingpoint of copper and beloW the maximum temperature attained, is such thatthe increasing temperature is higher than the increasing freezing point.Thus it may be said that the average rate of increase in the temperatureis greater than the average rate of elevation of the copper-nickel alloyformed by the solution of nickel into the copper.

`rous metal.

The rate does not have to be uniform throughout the range so long as thetemperature is maintained above the raising freezing point of theforming alloy. Also, the invention contemplates and provides a vmethodwherein the temperature is increased with such rapidity throughout thetemperature range below copper melting temperature as to preventcomplete diffusion of the copper and nickel in a solid state. 'Io thisend, it is preferable that the metals be heated by generation of heatwithin the metals as distinguished from the heating of the metals byradiation, although furnaces may be developed, such as the radiant tubefurnace, which will provide a suflicient temperature gradient to eiectheat transfer to the tube in a manner sufcient for the purpose.

A copper-nickel alloy which has the proportions of copper and nickel asare present in the metal known as Monel, has certain characteristicswhich are higher or more favorable than the characteristics of acopper-nickel alloy having a higher or lower percentage of nickel and acorresponding variation of copper. These characteristics include theyield strength, the ultimate strength, the working ability andcorrosion-resisting characteristics of the metal.`

Such a metal has about 67% to 70% of nickel and the remainder of copper,except for impurities which may include a small percentage of iron.Accordingly, for some purposes, it is preferable to provide a tube ofMonel metal. or in other words, a copper-nickel tube where thepercentages of copper and nickel approximate the percentagesfound inMonel. The tube need not be wholly made of copper-nickel strip but mayhave an inner ply or an outer ply formed by the copper-nickel strip andan outer ply or inner -ply respectively of cheaper 4or strength-givingmetal such as steel or other fer- In order to give such a tube thedesired characteristics' of having a high yield strength, ultimatestrength, 'working ability, corrosion resisting characteristics, etc.,it is necessary that the bond between the juxta-positioned parts havesimilar characteristics. To this end the invention contemplates a tubeand method of making a tube wherein the copper which is employed foreffecting the bond is so diffused with nickel that the seam itself orthe interfacial areas between the j'uxta-positioned parts in a seam orseams, or between plies, is a copper-nickel alloy approximating that ofthe strip. In carrying out the invention, commercially pure copper canbe employed, although cuprous metals such as brazing brasses and brazingbronzesmay be employed for tubes which are to be used -under less severeworking conditions and less severe conditions of use. e

The accompanying drawingy illustrates the method and shows illustrationsof the tubing.

Fig. 1 is a diagrammatic illustration showing the method where the tubeis heated by electrical induction.

Fig. 2 is a diagrammatic illustration showing the tube heated byelectrical resistance.

lagainst an off-set I in the stock which connects the inner and outerplies. Thus the off-set is at a non-abrupt angle with the beveled edgesin juxtaposition to opposite sides thereof. This geny eral form of tubeand the manner of making it is fully disclosed in the B. L. QuarnstromPatent No. 2,014,982 of September 17, 1935. In Fig. 4 a tube made fromtwo strips is shown. One strip forms an inner ply 5' with its edgesabutting in a seam 6; the other strip forms anl outer ply 1 and itsedges are preferably scarfed and overlapped in a seam at 8.

In Fig. 1 the strip may .be drawn from a supply roll I and may be passedthrough a tube mill having rolls illustrated at Il in which the strip isfashioned into tubular form.l The illustration in Fig. l shows the tubemade from a single strip, but the induction heating arrangement shown inFig` l can be employed for the double strip tube shown in Fig. 4. As thetube passes from the tube mill, it enters a heating zone, shown in Fig.1 as being in the form of a high frequency induction coil I2. Within thecoil is a quartz pipe I3 through which the tube passes, and after thetubefpasses through the heating zone it may pass through acoolingchamber I 4. Where desired, a suitable atmosphere, such as a reducing ornonoxidizing atmosphere, may be maintained by introducing the gas intothe quartz tube through an inlet pipe Il and into the cooler through aninlet pipe IB.

In Fig. 2 the final rolls of a tube mill are shown at 20 from which theformed tube passes into a chamber 2| where the tube is engaged byelectrodes 22 and 23 which may be opposed by idler rollers 2l and 25.The electric current thus passes lengthwise through the tube between theelectrode rollers 22 and 23 and the tube is heated by electricalresistance. As the tube leaves the chamber 2| it may pass through acooling chamber 28. A suitable non-oxidizing or reducing at mosphere maybe maintained by introducing a suitable gas into chamber 2l and cooler2B through inlet pipes 21 and 28.

The tubes shown in Figs. 3 and 4 are merely exemplary of a good manytubestructures which can be made. 'Ihe single strip of Fig. 3 will, ofcourse, be of the copper-nickel alloy. The tube of Fig. 4 may be madewith the inner ply of nickelcopper alloy and an outer ply of a cheapermetal such as a ferrous metal. On the other hand, the .tube shown inFig. 4 may have the outer ply of the nickel-copper alloy and the innerply of the cheaper ferrous metal. The use to which the tube is to be putmay determine whether the coppernickel alloy is on the inside or theoutside.

As the tube moves through the high frequency electrical mcoeuon heatingzone or Fig. 1. it is asedio? heated so that its temperature is raisedto above copper melting temperature with such rapidity as to prevent asubstantial diffusion of the copper and nickel in a solid state. In thisconnection, it is thought to be advisable to cite a given exemplarysituation. This example is as follows: The copper-nickel strip employedwas known as Monel metal having the proportions of copper and nickel asgiven above, and had a thickness of about .0145 inch so that whenfashioned into double ply tubing the wall thickness was about .028 inch.This copper-nickel strip was coated on both sides with copper, and theamount of copper was within the range of .l5 to .5 ounce for two squarefeet of surface. The copper was applied to the strip byelectrodeposition. It will be seen that with the tube thus fashionedthere will be a layer of copper on the outside of the tube and on theinside of the tube and between the plies and in the seam 4. This tubewas moved at a rate of about 20 feet per minute, while the inductioncoil had a total length of about 8 inches. The temperature of the tubewas raised rapidly and reached or exceeded copper melting temperature atabout the point indicated atX. This point was about two inches from theend of the induction coil. It will be seen, therefore, that thetemperature was raised from room temperature tor or exceeding coppermelting temperature in about one-half a second, and that the temperaturewas maintained above copper melting temperature at about two seconds, asthis is the time required for a given point on the tube to move throughthe inductor.

Now in the case of Monel metal, the temperature at which the same beginsto get soft or mushy is about 1315 C., whereas copper meltingtemperature is about 1084 C. It will be seen, therefore, that it isessential not to subject the tube to a temperature higher than thatwhich would melt the strip, but it must be considerably higher thancopper melting temperature, due to the dynamic nature of the situation.It is preferable, therefore, that the tube be heated rapidly to a pointsafely below l315 C. or say about 1300 C. However, it has been foundthat a satisfactory tube can be made where the temperature is in thevicinity of 1225 C. Thus the temperature'is raised from copper meltingtemperature to the maximum temperature attained at an average rategreater than the rate of elevation of the freezing point of thecopper-nickel alloyiormed as the copper and nickel enter into solution.Accordingly, temperatures considerably higher than copper meltingtemperature must be employed, and yet this temperature Vmust not exceedthe melting point of the copper-nickel alloy constituting the strip.

The form of tube shown in Fig. 4 requires the same rapid heating andtemperature conditions since the copper and the nickel of the inner orouterply diffuse with each other. In the Fig. 4 form, either the ferrousmetal strip or the coppernickel strip, or both, can be coated withcopper. However, it appears to be preferable to copper coat the ferrousmetal strip, as the coating protects the ferrous metal while it is' instrip form and -being handled in the shop, and because of a preliminarybond between the copper and the ferrous strip.

'The tube preferably has a metal composition or alloy at the interfacesin the seam or seams and between plies which approximates that of thelmetal of the strip. For example, a tube having maximum workingproperties and the ,other de- K desired as,

asedio? sirable characteristics of a Monel tube should be made of acopper-nickel strip having the percentages of copper and nickel whichapproximates that of Monel and likewise the vmetal in the seam or seamsand between plies should approximate the same percentages of copper andnickel. Otherwise, the seam or interfacial areas might be ruptured uponthe working of the tube. Under the conditions above recited, the copperand the nickel in the interfacial areas so diffused with each otherthat, according to the best available tests which can be made atpresent, the copper and nickel proportions were within about 2% of thatofthe original strip. In the making of the tube. the nickel in the stripat the interfacial areas alloys with the copper, and this results in abond between the parts or metal substantially like that of the strip.Accordingly, the nished tube, where it is made entirely fromcopper-nickel strip, has a substantially homogeneous characteristic. Atube structure like that of Fig. 3 made originally with an outsidediameter of about one-fourth or threeeighths of an inch has been drawndown to such a small size as to have a hole of about .0075 inch and awall thickness of .002 inch without rupture either of the metal of 'thestrip or the metal in the seams or plies.

The all nickel-copper tube has 'a large number of uses where corrosionresisting tubes are for example, in the chemical and dairy industries,cooling devices for beverages, radio antennas, particularly forautomotive vehicles and boats, and heat exchange devices of varioustypes. such a small size, it can be used in various places for controlpurposes as, for example, in thermostats 'or other heat sensitivedevices and for the so-called capillary tubes for refrigerating mecha-In the making of the composite tube as' shown n Fig. 4, the copper fillsin the butt joint at 6 to unite the steel interfaces where the inner plyis of steel, and to alloy with and unite the copper-nickel interfaceswhere the inner strip is of the copper-nickel alloy. Also, theinterfaces between the inner and outer plies are effectively united andthe scarfed seam 8 is united where the outer ply is of steelorcopper-nickel alloy. In this tube, it is preferablethat the copper sodiffuse with the nickel from the strip that the resultant composites ofthe metal at the interfaces approximates the proportions of the copperand nickel in the original strip. This composite tube may be employedwhere it is unnecessary to have corrosion resisting characteristics onboth the inner and outer surfaces of the tube.

' The compositetube can also be drawn down to very small sizes and canbe effectively employed for the purpose set forth above where it isnecessai-y to have the corrosion resisting metal only on one side of thetube. 1

Where a copper coated, copper-nickel alloy strip forms an outer ply, theexposed outer surface may have a somewhat spotty or roughenedappearance, but with the usual whitish appearance o1' the metal of thestrip: With the compsite tube as shown in Fim 4, the finished tube mayhave the copper coating intact o n the exposed surfaces of the steelregardless of whether or not the surfaces are on the outside or on theinside of the tube. i i

In the claims appended hereto the term copper is used in referenceto themetal which is supplied for sealingpurposes. This is to be conpliescomposed of a,

Since the tube can be reduced tov strued to' cover commercially purecopper and cuprous metals including the brazing brasses and bronzes.

Iclaim:

1. A tube comprising metal stock having the geometric shape of elongatedstrip with opposite edges, some of said metal stock being a coppernickelalloy, said metal stock being of hollow cross-sectional form havingparts, including the opposite edges, disposed in interfacialrelationship forming aseam or ply structure so that` the hollow form isclosed and a bond zone consisting entirely of an alloy of copper and thestrip stock metal cti-extensive with the interfaces and integraltherewith, said hond zone and the interface of the copper-nickel striphaving coppernickel proportions substantially corresponding to thecopper-nickel proportions of the coppernickel strip, whereby theproportions of copper and nickel throughout the body of the coppernickelstrip and the bond zone are substantially uniform. f

2. A tube comprising, copper-nickel 3. A tube comprising, metal stockhaving the' geometric shape of elongated strip with opposite 40 edges,said metal stock having copper and nickel proportions corresponding tothose proportions in Mone] metal, said metal stock being of hollowcross-sectional form having parts, including the opposite edges of thestrip and the opposite surfaces oi the strip, disposed in interfacialrelationship providing a seam and inner and outer ply structures to forma closed tubular wall and a bond z'one consisting entirely ofcopper-nickel alloy co`extensive with the interfaces and intgraltherewith, said bond zone and the interfaces having copper-nickelproportions substantially corresponding to the copper-nickel proportionsof the metal strip, whereby the copper-nickel proportions throughoutth'e thickness of the sf'tubular wall are substantially uniform.

4. A tube comprising, metal stock havingi the geometric shape ofelongated strip with opposite edges, some of the metal stock being 0fcoppernickel alloy and some being of ferrous metal, said metal /stockbeing of hollow cross-sectional form terfacial relationship to provide aseam and 'an inner and an outer ply structure to form a closed tubularwall and a bond zone consisting entirely' of copper-nickel-ferrousAalloy -co-extensive with' the interfaces and integral therewith, saidbond zone and the interface of the copper-nickel strip' RAYMOND n.Bonson alloy stock e having the geometric shape of the elongated strip-

